SUBMARINE FEATURES OF MODERN OPEN-SEA FAN DELTAS, HUON PENINSULA, PAPUA-NEW-GUINEA

A series of fan deltas has been delineated in water depths between 300 and 1900 m along the 75 km shelf and slope of the northern Huon Gulf, Papua New Guinea using the HAWAII MR1 side-scan system. Comparison of these fan deltas suggests that submarine slope profiles and feeder sy stems (i.e., type and size) are the most important factors controlling the construction and the geometry of the submarine fan deltas. Fan de ltas are fully developed only at large rivers in areas with a SS-shape d slope profile. Six zones are recognised on the SS-profiled fan delta surface based on the submarine topographic characteristics, dominant acoustic facies and slopes. The zonation differs from that of Prior an d Bornhold (1989) from fan deltas in a British Columbian fjord in term s of magnitude, slope profiles and submarine channelling patterns. The Huon fan deltas represent larger, more dynamic, deep-water delta syst ems with individual fan deltas up to 200 km(2). The main parts of the Huon fan deltas are deposited below 500 m, 5 km from river mouths. Lar ge quantities of coarse-grained sediments are found in water depths ov er 1400 m, 13 km from river mouths. The relief of the interfingered na rrow ridges and gullies in Zone 3 is up to 100 m. Zone 6 has a slope g radient of 4.4 degrees, much steeper than Zone 5 (1.5 degrees). The Hu on fan deltas can not be easily fitted into any of the existing classi fication. They warrant a comparative study of fan deltas with similar feeder systems but different slope profiles, and with similar slope pr ofiles but different feeder systems in the same basin regime. Delta cl assification and nomenclature needs to reflect seven attributes: feede r system, basin dynamics, water depth (depth ratio), slope profile, do minant slope process, delta-front grain size and geometry.